System and method for axial zoning of heating power

ABSTRACT

A heater system for an exhaust system is provided. The heater system includes a heater disposed in an exhaust conduit. The heater includes a plurality of heating elements disposed in the exhaust conduit. A heating control module controls the plurality of heating elements differently according to operating conditions specific to each heating element. In other forms, the heater system for an exhaust system has a plurality of heating zones, instead of a plurality of heating elements. The heating control module controls the plurality of heating zones differently according to operating conditions specific to each heating zone.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. patentapplication Ser. No. 15/448,044, filed on Mar. 2, 2017, which claimspriority to and the benefit of U.S. provisional application Ser. No.62/302,482, filed on Mar. 2, 2016, the contents of U.S. patentapplication Ser. No. 15/448,044 and U.S. provisional application Ser.No. 62/302,482 are incorporated herein by reference in their entirety.This application is also related to the following applications: U.S.application Ser. No. 15/448,186 titled “Bare Heating Elements forHeating Fluid Flows,” U.S. Pat. No. 1,0544,722 titled “Virtual SensingSystem,” U.S. application Ser. No. 15/447,964 titled “Heater Element asSensor for Temperature Control in Transient Systems,” U.S. applicationSer. No. 15/447,994 titled “Heater Element Having Targeted DecreasingTemperature Resistance Characteristics,” U.S. application Ser. No.15/448,068 titled “Dual-Purpose Heater and Fluid Flow MeasurementSystem,” U.S. application Ser. No. 15/448,162 titled “Heater-ActuatedFlow Bypass,” U.S. Pat. No. 10,470,247 titled “Susceptor for Use in aFluid Flow System,” and U.S. application Ser. No. 15/448,130 titled“Thermal Storage Device for Use in a Fluid Flow System,” all of whichwere filed on Mar. 2, 2017 and are commonly assigned with the presentapplication, the contents of which are incorporated herein by referencein their entirety.

FIELD

The present disclosure relates to heating and sensing systems for fluidflow applications, for example vehicle exhaust systems, such as dieselexhaust and aftertreatment systems.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

The use of physical sensors in transient fluid flow applications such asthe exhaust system of an engine is challenging due to harshenvironmental conditions such as vibration and thermal cycling. Oneknown temperature sensor includes a mineral insulated sensor inside athermowell that is then welded to a support bracket, which retains atubular element. This design, unfortunately, takes a long amount of timeto reach stability, and high vibration environments can result in damageto physical sensors.

Physical sensors also present some uncertainty of the actual resistiveelement temperature in many applications, and as a result, large safetymargins are often applied in the design of heater power. Accordingly,heaters that are used with physical sensors generally provide lower wattdensity, which allows a lower risk of damaging the heater at the expenseof greater heater size and cost (same heater power spread over moreresistive element surface area).

Moreover, known technology uses an on/off control or PID control from anexternal sensor in a thermal control loop. External sensors haveinherent delays from thermal resistances between their wires and sensoroutputs. Any external sensor increases the potential for componentfailure modes and sets limitations of any mechanical mount to theoverall system.

One application for heaters in fluid flow systems is vehicle exhausts,which are coupled to an internal combustion engine to assist in thereduction of an undesirable release of various gases and other pollutantemissions into the atmosphere. These exhaust systems typically includevarious after-treatment devices, such as diesel particulate filters(DPF), a catalytic converter, selective catalytic reduction (SCR), adiesel oxidation catalyst (DOC), a lean NO_(x) trap (LNT), an ammoniaslip catalyst, or reformers, among others. The DPF, the catalyticconverter, and the SCR capture carbon monoxide (CO), nitrogen oxides(NO_(x)), particulate matters (PMs), and unburned hydrocarbons (HCs)contained in the exhaust gas. The heaters may be activated periodicallyor at a predetermined time to increase the exhaust temperature andactivate the catalysts and/or to burn the particulate matters orunburned hydrocarbons that have been captured in the exhaust system.

The heaters are generally installed in exhaust pipes or components suchas containers of the exhaust system. The heaters may include a pluralityof heating elements within the exhaust pipe and are typically controlledto the same target temperature to provide the same heat output. However,a temperature gradient typically occurs because of different operatingconditions, such as different heat radiation from adjacent heatingelements, and exhaust gas of different temperature that flows past theheating elements. For example, the downstream heating elements generallyhave a higher temperature than the upstream elements because thedownstream heating elements are exposed to fluid having a highertemperature that has been heated by the upstream heating elements.Moreover, the middle heating elements receive more heat radiation fromadjacent upstream and downstream heating elements.

The life of the heater depends on the life of the heating element thatis under the harshest heating conditions and that would fail first. Itis difficult to predict the life of the heater without knowing whichheating element would fail first. To improve reliability of all theheating elements, the heater is typically designed to be operated with asafety factor to reduce and/or avoid failure of any of the heatingelements. Therefore, the heating elements that are under the less harshheating conditions are typically operated to generate a heat output thatis much below their maximum available heat output.

SUMMARY

The present disclosure provides for a heater system for an exhaustsystem including a heater disposed in an exhaust conduit of the exhaustsystem. The heater includes a plurality of heating elements disposedalong an axial direction of the exhaust conduit. The heater systemincludes a heater control module operable to control at least two of theplurality of heating elements differently with respect to each otheraccording to at least one operating condition specific to at least twoof the plurality of heating elements.

In another form, a heater system for an exhaust system is provided thatincludes a heater disposed in an exhaust conduit of the exhaust system.The heater includes a plurality of zones disposed along an axialdirection of the exhaust conduit. The system further includes a heatercontrol module operable to control at least two of the plurality ofheating zones differently with respect to each other and according to atleast one operating condition specific to at least two of the pluralityof heating zones.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now bedescribed various forms thereof, given by way of example, referencebeing made to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a diesel engine and exhaustaftertreatment system in which the principles of the present disclosureare applied;

FIG. 2 is a perspective view of a heater assembly installed in anupstream exhaust conduit and constructed according to the teachings ofthe present disclosure;

FIG. 3 is a perspective, cross-sectional view of the heater assemblyinstalled in an upstream exhaust conduit of FIG. 2;

FIG. 4 is a perspective, cross-sectional view of another heaterassembly, showing a temperature distribution in the flow direction;

FIG. 5 is a schematic view of a heater control module of a heatingsystem constructed and operating in accordance with the teachings of thepresent disclosure; and

FIG. 6 is a graph comparing the maximum available power and actual poweroutput of each heating element to achieve a uniform temperature acrossthe heating elements of the heater assembly.

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

Referring to FIG. 1, an exemplary engine system 10 generally includes adiesel engine 12, an alternator 14 (or generator in some applications),a turbocharger 16, and an exhaust aftertreatment system 18. The exhaustaftertreatment system 18 is disposed downstream from a turbocharger 16for treating exhaust gases from the diesel engine 12 before the exhaustgases are released to atmosphere. The exhaust aftertreatment system 18can include one or more additional components, devices, or systemsoperable to further treat exhaust fluid flow to achieve a desiredresult. In the example of FIG. 1, the exhaust aftertreatment system 18includes a heating system 20, a diesel oxidation catalyst (DOC) 22, adiesel particulate filter device (DPF) 24, and a selective catalyticreduction device (SCR) 26. The exhaust aftertreatment system 18 includesan upstream exhaust conduit 32 that receives a heater assembly 28therein, an intermediate exhaust conduit 34 in which the DOC 22 and DPF24 are provided, and a downstream exhaust conduit 36 in which the SCR 26is disposed.

It should be understood that the engine system 10 illustrated anddescribed herein is merely exemplary, and thus other components such asa NO_(x) adsorber or ammonia oxidation catalyst, among others, may beincluded, while other components such as the DOC 22, DPF 24, and SCR 26may not be employed. Further, although a diesel engine 12 is shown, itshould be understood that the teachings of the present disclosure arealso applicable to a gasoline engine and other fluid flow applications.Therefore, the diesel engine application should not be construed aslimiting the scope of the present disclosure. Such variations should beconstrued as falling within the scope of the present disclosure.

The heating system 20 includes a heater assembly 28 disposed upstreamfrom the DOC 22, and a heater control module 30 for controllingoperation of the heater assembly 28. Heater assembly 28 can include oneor more electric heaters wherein each electric heater includes at leastone resistive heating element. The heater assembly 28 is disposed withinan exhaust fluid flow pathway in order to heat the fluid flow duringoperation. Heater control module 30 typically includes a control deviceadapted to receive input from the heater assembly 28. Examples ofcontrolling the operation of the heater assembly 28 can include turningthe heater assembly on and off, modulating power to the heater assembly28 as a single unit and/or modulating power to separate subcomponents,such as individual or groups of resistive heating elements, ifavailable, and combinations thereof.

In one form, the heater control module 30 includes a control device. Thecontrol device is in communication with at least one electric heater ofthe heater assembly 28. The control device is adapted to receive atleast one input including but not limited to an exhaust fluid flow, massvelocity of an exhaust fluid flow, flow temperature upstream of the atleast one electric heater, flow temperature downstream of the at leastone electric heater, power input to the at least one electric heater,parameters derived from physical characteristics of the heating system,and combinations thereof. The at least one electric heater can be anyheater suitable to heat an exhaust fluid. Example electric heatersinclude but are not limited to a band heater, a bare wire resistiveheating element, a cable heater, a cartridge heater, a layered heater, astrip heater, and a tubular heater.

The system of FIG. 1 includes the DOC 22 disposed downstream from theheater assembly 28. The DOC 22 serves as a catalyst to oxidize carbonmonoxide and any unburnt hydrocarbons in the exhaust gas. In addition,the DOC 22 converts nitric oxide (NO) into nitrogen dioxide (NO₂). TheDPF 24 is disposed downstream from the DOC 22 to assist in removingdiesel particulate matter (PM) or soot from the exhaust gas. The SCR 26is disposed downstream from the DPF 24 and, with the aid of a catalyst,converts nitrogen oxides (NOx) into nitrogen (N₂) and water. A ureawater solution injector 27 is disposed downstream from the DPF 24 andupstream from the SCR 26 for injecting urea water solution into thestream of the exhaust gas. When urea water solution is used as thereductant in the SCR 26, NOx is reduced into N₂, H₂O and CO₂.

Referring to FIGS. 2 and 3, one form of the heater assembly 28 is shownto be disposed in the exhaust conduit 32 and includes a plurality ofheating elements 38. The heating elements 38 may be in the form ofheating coils, such as a tubular heater as illustrated herein, arrangedalong a longitudinal axis X of the upstream exhaust conduit 32. Theplurality of heating elements 38 may be provided in any type ofconstruction such as a band heater, a bare wire resistive heatingelement assembly, a cable heater, a cartridge heater, a layered heater,a strip heater, or a tubular heater, among others. Accordingly, theillustration of a tubular heater should not be construed as limiting thescope of the present disclosure. In one form, the heater assembly 28 ismounted to the upstream exhaust conduit 32 by brackets 40. In anotherform, the heater assembly 28 may include a plurality of heating zonesdisposed along an axial direction of the upstream exhaust conduit. Eachheating zone includes at least one resistive heating element.

The plurality of heating elements 38 may exhibit predeterminedperformance characteristics by measurement or estimation. Theperformance characteristics of the plurality of heating elements 38include a heat flux density for the plurality of heating elements 38 ata given voltage or under a specified process flow condition. Heat fluxis the rate of heat energy transfer through a given surface per unittime. Heat flux density is the heat rate per unit area as measured inWatt density (watts/mm²). Heat flux or heat flux density provides usefulinformation for predicting performance of the plurality of heatingelements 38, including temperature, transfer efficiency, and life (andconsequently reliability). A heating element 38 with a higher fluxdensity generally provides a faster temperature rise and has a smallersurface area (and consequently lower manufacturing costs) than a heatingelement 38 with a lower higher flux density. However, a heating element38 with a higher flux density generally has a reduced life and lowerreliability due to higher thermal stress and fatigue.

Referring to FIG. 4, when the exhaust gas flows through the heaterassembly 28 including a plurality of heating elements 38, thetemperature of the exhaust gas at the upstream heating elements 42 isgenerally lower than that of the exhaust gas at the downstream heatingelements 44. If the upstream and downstream heating elements 42, 44 arecontrolled to generate the same heat flux, the upstream heating elements42 generally has a lower temperature than the downstream heating element44 because the flow upstream of the heating elements 38 has not beenheated. However, if the upstream heating elements 42 are controlled tothe same temperature to output higher heat flux density than thedownstream heating element 44, the increased heat flux density at theupstream heating elements 42 will cause higher heating and cooling ratesfor the upstream heating elements 42 at various points in the cycle,leading to higher thermal stress and shorter life due to thermalfatigue.

Therefore, instead of simply increasing the heat flux density of theupstream heating elements 42, the heater control module 30 of thepresent disclosure actively controls the plurality of heating elements38 independently to provide a desired heating cycle, heating rate, andtarget temperature, based on operating parameters specific to theplurality of heating elements 38, taking into consideration the thermalgradient across the plurality of heating elements 38 and the differentheat radiation, to improve heater performance while providing improvedreliability. It should be understood that the heater control module 30may control at least two of the heating elements 38 independently, orany of a plurality of heating elements 38 independently, or each of theheating elements 38 independently while remaining within the scope ofthe present disclosure.

The plurality of heating elements 38 may be designed to have the samephysical properties, and consequently the same heat flux density at agiven power level, to simplify manufacturing and control of the heaterassembly 28. Alternatively, the plurality of heating elements 38 may bedesigned to have different sizes and physical properties to providedifferent watt densities at a given power level. In either case, theplurality of heating elements 38 are controlled by the heater controlmodule 30 to provide different heat flux densities in view of thethermal gradient and heat radiation for improved reliability of theheater assembly 28.

Referring to FIG. 5, the heater control module 30 controls the pluralityof heating elements 38 of the heater assembly 28 differently withrespect to each other according to at least one operating conditionspecific to each of the plurality of heating elements 38 to achieveimproved heating performance and reliability. The heater control module30 includes an operating parameter acquiring module 50, a reliabilitydetermination module 52, a target temperature and heating cycledetermination module 54, and a power control and switching module 56.Optionally, the heater control module 30 may include a virtual sensingmodule 58 and a heater performance characteristics data storage module59 set forth above. It should also be understood that the variousmodules, including by way of example the reliability determinationmodule 52, the target temperature and heating cycle determination module54, and the virtual sensing module 58, among others, may be optional.

The operating parameters acquiring module 50 acquires operatingparameters specific to at least one of the plurality of heating elements38 from a plurality of sensors 60, 62, 64. The parameters include, butare not limited to, temperature of the heating element 38 measured by atemperature sensor 60 (or calculated), and the flow rate of the exhaustgas measured by a flow rate sensor 62.

The virtual sensing module 64 may receive data from an engine controlmodule (ECM) 64 to estimate or predict some operating parameters,resulting in a virtual sensing of some of the operating parameters. Forexample, the data obtained from the ECM 64 may include exhaust flow rateand heater inlet temperature. The virtual sensing module 58 may estimatethe heater outlet temperature based on the data from the ECM 64. Theestimated data can be sent to the operating parameter acquiring module50 for a more accurate reliability estimation.

In some applications, the exhaust system may be operated under differentmodes such as normal (no active regeneration but possibly passiveregeneration); heating mode (or warm-up mode)—the engine raisesaftertreatment temperature to achieve active regeneration; cold mode (orcold start mode)—NOx is actively stored in a low-temperature condition;heavy load mode—allows the release of the stored NOx, at higher exhausttemperatures. Additional modes of operation are described in U.S.published patent application no. 2014/0130481, which is herebyincorporated by reference in its entirety.

The virtual sensing module 58 can receive operating parameters of atleast one of the plurality of heating elements 38. For instance, thevirtual sensing module 58 can receive information about a particularmode and estimate outlet temperature of each heating element 38 toincrease accuracy of potential heat flux density available to eachheating element 38. Therefore, the virtual sensing module 58 mayestimate a temperature coming out of each heating element 38, which isthe inlet temperature to the next heating element 38, instead of onlyknowing the inlet temperature used for each heating element 38. Thetemperature estimation may be based on energy balance (conservation ofenergy) to predict the outlet temperature of each heating element 38,including losses to the surrounding environment.

The reliability determination module 52 determines reliability of eachheating element 38 for a particular power level based on the operatingparameters specific to each heating element 38. The reliabilitydetermination module 52 may receive data from the heater performancecharacteristics data storage module 59 that stores performancecharacteristics data specific to the individual heating elements 38.While the plurality of heating elements 38 may be manufactured accordingto the same specifications, each heating element 38 may not provide thesame heating performance, such as heat flux density, due tomanufacturing variations and deviations. Therefore, parameters relatingto manufacturing variations and deviations may be predetermined andstored in the heater performance characteristics data storage module 59and are provided to the reliability determination module 52 for a moreaccurate reliability calculation.

The reliability of each heating element 38 may also be affected by otherfactors, such as vibration or physical loads imposed by the mountingbracket 40 that mounts the heater assembly 28 to the upstream exhaustconduit 32. Whether a heating element 38 also serves as a structuralmember affects the reliability of the heating element 38. Therefore, theeffects of these factors may be pre-stored in the heater performancecharacteristics data storage module 59 for a more accurate reliabilitydetermination.

The reliability determination module 52 may determine the expectedreliability for the plurality of heating elements 38 based on arelationship between the reliability and the operating parameters. Thisrelationship may be directly available for an upstream heating element42 based on empirical data or experimentation. For example, therelationship may be obtained by performing Calibrated Accelerated LifeTesting (CALT) of the heating element 38. Accelerated life testing isthe process of testing a product by subjecting it to conditions such asstress, strain, temperatures etc. in excess of its normal serviceparameters in an effort to uncover faults and potential modes of failurein a short amount of time. In the present form, CALT may be used toprovide a relationship between the heating cycle and the time for agiven power level or a given operating environment. Therefore, CALTprovides a relationship between reliability and the operating parametersfor each heating element 38. The reliability data may be provided onlyfor the heating element 38 that experiences more harsh operatingconditions.

After the reliability of the upstream and downstream heating elements42, 44 is determined, the reliability determination module 52 determinesthe average reliability by averaging the reliability of the upstream anddownstream heating elements 42, 44. The information regarding theaverage reliability is sent to the target temperature and heating cycledetermination module 54.

The target temperature and heating cycle determination module 54calculates the target temperature of the upstream and downstream heatingelements 42, 44 as well as the heating cycle based on the same averagereliability. The target temperature would allow the plurality of heatingelement 38 to achieve the same average reliability. For intermediateheating elements 39, interpolation between the values from the upstreamand downstream heating elements 42, 44 may be used to determine a targettemperature.

The target temperature and heating cycle determination module 54calculates target temperatures for each heating element 38 to obtain thesame average reliability for a given desired power level and flow rate.The target temperature may be constantly updated in response to a changein power level that may change over time, among changes in other systemvariables. This dynamic calculation would allow a more accuratedetermination of the target temperatures for a heating element 38 basedon a plurality of parameters, including but not limited to actual flowrate, power level, and design values for these quantities. Therefore,the reliability of a given heater assembly 28 in an operating heatingsystem 20 can be improved.

The target temperature and heating cycle determination module 54 canalso perform a real-time target temperature calculation for improvedreliability. For example, the reliability determination module 52 maydetermine the effect of di/dt (change in current over time, or dV/dt,change in voltage over time) on heater reliability and the impact ofswitching frequency for a desired power level. The target temperatureand heating cycle determination module 54 then determines a targettemperature corresponding to the desired power level with higherreliability. The target temperature and heating cycle determinationmodule 54 also determines the number of heating cycles to maintain theparticular target temperatures for the various heating elements 38 toproduce the desired power level with higher reliability.

In another form, the target temperature and heating cycle determinationmodule 54 may be two modules. The power control and switching module 58controls the power level provided to each heating element 38 andswitches the heating elements 38 based on the calculated heating cycleto achieve the target temperature. The power control and switchingmodule 56 controls switching of the heating elements 38 between an “on”state and an “off” state based on the calculated heating cycle. Theaverage power density can be reduced to a level to provide improvedreliability of the heating elements 38. Faster switching would generallyfacilitate longer life, but the rate of switching can be selected toimprove durability. Each heating element 38 can be controlled to have amaximum average heat flux density while ensuring optimum reliability ofthe heating elements 38.

The heater control module 30 controls and varies heat flux density ofthe heating elements 38 based on their axial position in the upstreamexhaust conduit 32 to maintain a constant durability across theplurality of heating elements 38 while increasing the total combinedheat flux density across all heating elements 38. The varied heat fluxdensity from the first to subsequent heating elements 38 can maintain aconstant durability and increase power within a smaller physical spaceby setting the target temperature differently in different zones.Accordingly, the heating elements 38 can be operated to provideincreased available heat flux density while maintaining constantdurability/reliability across the plurality of heating elements 38. Asafety factor may not be required because the operating parametersspecific to a particular heating element 38 are closely monitored andthe heat output for optimum reliability is constantly adjusted.

The plurality of heating elements 38 may be controlled to have differenttarget temperatures, thereby generating different heat output (heat fluxdensity) to maintain a uniform temperature of the plurality of heatingelements 38, taking into consideration of parameters specific to eachheating element 38. Each heating element 38 can be designed to have thesame large heat flux density and can be turned on to full-power at thesame time during engine cold start. After the heating elements 38 reachthe target temperature, the heating elements 38 can be switched down toan appropriate power level to maintain the heating element 38 at thetarget temperature. Therefore, the heater assembly 28 can generate alarger heat flux density to rapidly heat the exhaust gas and theindividual heating elements 38 may be turned off when safety limits arereached.

Referring to FIG. 6, the graphs show the heater assembly 28 thatincludes a plurality of axially arranged heating elements 38 can haveeach heating element 38 designed to have the same high-power level, asindicated by bars A. The heating elements 38 can be switched down to theappropriate level, as indicated by bars B, when the material temperaturelimits are reached, or other operating parameters dictate reduced power.Bars B also indicate the heater power of each heating element 38 atsteady state or a simple transient that maintains a constant sheathtemperature. Durability of each heating element 38 may be affected bynumber and magnitude of thermal cycles as well as a transient condition,such as di/dt (change in current over time). The maximum kW for eachheating element 38 can vary based on transient conditions. For example,a much higher power density can be utilized for a shorter period of timewhen the heating element 38 is cold. The power density can be reduced astime increases. In addition, the rate of applying power to the heatingelements 38 can be adjusted to be slower to prevent damage to the heaterassembly 28. Therefore, the heater control module 30 includes a controlalgorithm to take the transient condition of at least one of theplurality of heating elements 38 into consideration to improvedurability/reliability. By using a heater control module 30 to controlturning on and off and powering up and down of the individual heatingelements 38, the heater performance can be optimized based on operatingconditions and limitations on the heater structure such as capacity ordurability, thereby obtaining an optimum reliability of all heatingelements 38.

The present disclosure has the advantages of generating more heat fluxdensity in a smaller area. The increased heat flux density can result inreduced size of the heating elements 38, a reduced cost of the heatingelements 38 and faster heating during engine cold start. Therefore, thepresent disclosure balances the reliability, size and power output ofthe heating elements 38 for a multi-zone heater assembly 28, therebyachieving an improved heating result.

The present disclosure can also accommodate transient conditions, aswell as provide a better adaptation to a failed heating element 38. If aheating element 38 or its related power components fail, the remainingheating elements 38 can be controlled to supply a portion of the lostpower. When a heating element 38 has a lower reliability, or if theheating element 38 fails, the particular heating element 38 can bepowered to reduce the heat flux density. The output of the remainingheating elements 38 can be adjusted to compensate for the reduced heatflux from the particular heating element 38. Therefore, the entireheater assembly 28 can still generate the desired overall power outputwithout subjecting the particular heater to reduced reliability.

In yet another form of the present disclosure, the heating elements 38can be controlled to provide a desired increased watt density (havingsmaller sizes, thereby reducing manufacturing costs). The heat fluxoutput from the individual heating elements 38 may be controlleddifferently and adjusted during operation according to the operatingdata acquired by the operating parameters acquiring module 50. The heatflux from each heating element 38 may be changed by using the powercontrol and switching module 56 to switch the heating elements 38 “on”and “off” to achieve a desired heat flux and improved reliability. Theheating system 20 allows for a smaller (thus less costly) heatingelement 38 for a given power level and desired reliability level. Foreach heating element 38, the temperature of the heating element 38, thedifference between the maximum and minimum temperature, the maximumcooling rate, the number of heating cycles (both “control cycles” and“machine cycles”), and the maximum power or heating rate can be trackedover time. The heat output from the heating elements 38 may be adjustedaccording to these varied parameters.

Although a fluid flow application of a diesel exhaust has beenillustrated and described herein, it should be understood that thevarious forms of axial heating may be applied to any number ofapplications and to provide a variety of heating/power distributions, orsystem functionality, along a fluid flow. For example, axial heatingcould be employed to vary power density from one heating element tosubsequent heater elements in order to increase power in a smallerphysical space. In another form, power density could be varied tomaintain a constant element sheath or wire temperature. Still further, amap of axial power distribution at different engine speeds and torquescould be created, and then power variations could be controlled based onactual engine conditions in use. Accordingly, the various formsillustrated and described herein should not be construed as limiting thescope of the present disclosure.

The description of the disclosure is merely exemplary in nature and,thus, variations that do not depart from the substance of the disclosureare intended to be within the scope of the disclosure. Such variationsare not to be regarded as a departure from the spirit and scope of thedisclosure.

What is claimed is:
 1. A heater system for an exhaust system of aninternal combustion engine, the heater system comprising: a heaterdisposed in an exhaust conduit of the exhaust system, the heaterincluding a plurality of heating elements disposed along an axialdirection of the exhaust conduit; and a heater control module operableto actively control power being supplied to at least two heatingelements among the plurality of heating elements differently withrespect to each other according to at least one operating conditionspecific to the at least two heating elements among the plurality ofheating elements, wherein the at least two heating elements includes afirst upstream heating element and a first downstream heating elementand the heater control module controls the first upstream heatingelement to be at a higher power level than the first downstream heatingelement.
 2. The heater system according to claim 1, wherein theplurality of heating elements includes a plurality of upstream heatingelements, including the first upstream heating element, that aredisposed upstream in the exhaust conduit and a plurality of downstreamheating elements, including the first downstream element, that aredisposed downstream in the exhaust conduit.
 3. The heater systemaccording to claim 2, wherein the heater control module controls theplurality of upstream heating elements at a higher power level than theplurality of downstream heating elements.
 4. The heater system accordingto claim 3, wherein the heater control module includes an operatingparameter acquiring module operable to acquire operating parameters ofat least one heating element of the plurality of heating elements. 5.The heater system according to claim 3, wherein the heater controlmodule includes a virtual sensing module operable to acquire operatingparameters of at least one heating element of the plurality of heatingelements.
 6. The heater system according to claim 3, wherein the heatercontrol module includes a heater performance characteristics datastorage module operable to store operating parameters of at least oneheating element of the plurality of heating elements.
 7. The heatersystem according to claim 3, wherein the heater control module includesa reliability determination module operable to determine reliability ofat least one heating element of the plurality of heating elementsaccording to operating conditions of the at least one heating element ofthe plurality of heating elements.
 8. The heater system according toclaim 7, wherein the reliability determination module determines anaverage reliability of the plurality of heating elements.
 9. The heatersystem according to claim 7, wherein the heater control module includesa target temperature and heating cycle determination module operable todetermine a target temperature for each heating element based on one ofthe following: the determined reliability, a different targettemperature, a heating cycle, or combinations thereof.
 10. The heatersystem according to claim 9, wherein the heater control module includesa power control and switching module operable for controlling a powerlevel provided to each heating element of the plurality of heatingelements and switching each heating element of the plurality of heatingelements on and off based on the determined heating cycle sufficient toachieve the target temperature.
 11. The heater system according to claim3, wherein the heater control module includes a control algorithm todetermine transient conditions of at least one heating element of theplurality of heating elements.
 12. The heater system according to claim3, wherein the heater control module is operable to control each heatingelement of the plurality of heating elements to reach one of thefollowing: a different target temperature, a different heating cycle, orcombinations thereof.
 13. The heater system according to claim 1,wherein the heater control module is configured to provide power to thefirst upstream heating element at the same time as providing power tothe first downstream heating element so that the first upstream heatingelement is at the higher power level than the first downstream heatingelement.
 14. A heater system for an exhaust system of an internalcombustion engine, the heater system comprising: a heater disposed in anexhaust conduit of the exhaust system, the heater including a pluralityof heating zones disposed along an axial direction of the exhaustconduit; and a heater control module operable to actively control powerbeing supplied to at least two heating zones among the plurality ofheating zones differently with respect to each other and according to atleast one operating condition specific to the at least two heating zonesamong the plurality of heating zones, wherein the at least two heatingzones includes a first upstream heating zone and a first downstreamheating zone and the heater control module controls the first upstreamheating zone to be at a higher power level than the first downstreamheating zone.
 15. The heater system according to claim 14, wherein theplurality of heating zones includes a plurality of upstream heatingzones, including the first upstream heating zone, that are disposedupstream in the exhaust conduit and a plurality of downstream heatingzones, including the first downstream heating zone, that are disposeddownstream in the exhaust conduit.
 16. The heater system according toclaim 15, wherein the heater control module controls the plurality ofupstream heating zones at a higher power level than the plurality ofdownstream heating zones.
 17. The heater system according to claim 16,wherein the heater control module includes a reliability determinationmodule operable to determine reliability of at least one heating zone ofthe plurality of heating zones according to the operating conditions ofat least one heating zone of the plurality of heating zones.
 18. Theheater system according to claim 17, wherein the heater control moduleincludes a target temperature and heating cycle determination moduleoperable to determine a target temperature for each heating zone basedon one of the following: the determined reliability, a targettemperature, a heating cycle, or combinations thereof.
 19. The heatersystem according to claim 18, wherein the heater control module includesa power control and switching module operable to control power providedto the heater and switching on and off each heating zone of theplurality of heating zones based on the determined heating cyclesufficient to achieve the target temperature.
 20. The heater systemaccording to claim 16, wherein the heater control module is operable toactively control each heating zone of the plurality of heating zones toreach one of the following: different target temperatures, differentheating cycles, or combinations thereof.